An interesting quote from an interesting article

Because you can't tell a great hacker except by working with him, hackers themselves can't tell how good they are. This is true to a degree in most fields. I've found that people who are great at
something are not so much convinced of their own greatness as mystified at why everyone else seems so incompetent. The people I've met who do great work rarely think that they're doing great work. They generally feel that they're stupid and lazy, that their brain only works properly one day out of ten, and that it's only a matter of time until they're found out.

From: http://www.paulgraham.com/gh.html